If combustible gas and oxidising agent (e.g. hydrogen and oxygen) meet from opposite directions, their impulses are at least partially cancelled out. Thus, a flame front, which can be not only of an elongated shape but also of a spherical shape, is achieved. This is not the case with a premix flame since both gases flow basically in one direction there. Also, a diffusion flame is less advantageous since diffusion has to take place there. The flame is also at a distance from the nozzles so that only a small amount of heat is dissipated via the nozzles. Lower gas velocities, especially lower exhaust gas velocities, are also possible, as a result of which heat losses are reduced as a result of forced convection.
All this contributes towards increasing the flame temperature in the process. Finally, a longer residence time of the sample gas to be analysed in the combustion chamber is also achieved. The spherical shape is especially favourable for the flame stability on account of the minimum surface over which the heat is dissipated in comparison to the volume in which the heat is generated.
This is extremely important if the aim is to use only very small flames, as is necessary in miniaturised scientific instruments or gas detectors, for example. Miniaturized counterflow burners, in which the combustion chamber is encompassed by a capillary consisting of stainless steel, are known for such analyses (US2005/0287033A1, US2008/0213908A1). The production of corresponding small capillaries is certainly possible. The assembly of corresponding counterflow burners, which consist of different parts, gives rise to considerable difficulties and costs, however, especially when the desire would be to use structures which are as small as possible and when these are to be produced in batch production. Furthermore, a capillary extends only in one direction, that is to say it is an essentially one-dimensional structure, so that only comparatively few ways exist of influencing the flame.
These micro-counterflow burners are used for example for photometric gas chromatography and gas chromatography with measurement of the generated ionisation. Corresponding devices can serve in this case not only for scientific purposes but are also suitable, for example, for being used in environmental technology in order to determine harmful gases.
The object of the invention exists in the creation of a counterflow burner of small dimensions which is to be inexpensively produced.